It is common and universal for low frequency application transformers and other inductive devices to be made up of a magnetic core comprising a plurality of sheets of steel, the sheets being die cut and stacked to create the desired thickness of a core. For many years the thickness (thus number of necessary pieces) of the stampings has been determined by a strict set of constraints-magnitude of eddy currents versus number of necessary pieces. For that reason, individual sheets of selected thickness are oxide-coated, varnished or otherwise electrically insulated from one another in order to reduce/minimize eddy currents in the magnetic core.
The magnetic core of a transformer or the like generally passes through the center of the electric winding, and closes on itself to provide a closed magnetic circuit. Since the magnetic core then supports the electric windings, it is natural that the core has also been used as the support for the transformer. That is to say, one attaches the magnetic core to a container or baseboard in order to support the transformer.
Transformers and other inductive devices inherently generate heat, and the heat must be dissipated or the power characteristics of the device will change. If the transformer or other device becomes too hot, the electric windings can become short circuited and burn out. In small devices, one usually relies on air cooling, sometimes with metal fins/heat sinks or the like to assist in dissipating the heat. In large devices, the windings and magnetic core may be cooled by forced air or immersed in an oil or other fluid. One then may use fins on the container, radiator pipes, or both, so convection currents move the heated fluid through the cooling fins or pipes. If further cooling is needed, one generally resorts to pumps to force fluid movement and/or fans to move more air across the cooling means.
When a stack of metal sheets is used as the magnetic core for an inductive device, it is usual to provide a shape, such as an E with the electric windings on the center leg of the E. After the windings are in place, an additional stack of sheets usually in an I configuration is applied to connect the ends of the E, thereby completing the magnetic circuit. Using such a technique, it will be understood that the windings are necessarily wound separately, and subsequently placed on the magnetic core. The windings must therefore be large enough to slip onto the magnetic core. Such construction contributes to the inherent noisiness of an inductive device. because the electric windings must be somewhat loose on the core. As a result, when an alternating voltage is applied to the electric windings, the sheets making up the core tend to vibrate with the alternating magnetic field or in sympathy in a subharmonic. Any resulting gaps and spaces between the electrical components and the magnetic components also reduce coupling and efficiency of action.
Transformers and other inductive devices also inherently generate electromagnetic fields. Such fields external to the device lessen efficiency, as well as pose interferences to the immediately surrounding environment. Although the strength of these electromagnetic fields decreases with distance from the transformer, shielding of either the electromagnetic field source or the affected components is often required. As components in today's electronics are made more sensitive and their packaging more dense, susceptibility to electromagnetic interaction increases dramatically. To assure optimum performance of these components, stray electromagnetic fields must be minimized often at a substantial cost. As noted above, one manner in which these fields may be minimized is to provide shielding around the source in order to contain the electromagnetic fields and to prevent interference from external sources.
Thus, an important aspect of the present invention is to provide a shielded wire core inductive device, such as a transformer, in an efficient and cost effective manner.